|
|
9 March 2004 Intoduction of Cycle 28r1.
This version includes the following mainly minor, technical modifications
:
- Data assimilation changes:
- new snow analysis using NESDIS snow cover product;
- Improved use of Goes BUFR winds;
- Improved clouds in 4D-Var minimisation;
- Re-introduction of ERS-2 scatterometer winds (with adjusted
pre-screening and limited coverage) .
- Variational QC corrected for 3D-Var (with impact of the BC
project and ERA-40 reruns only);
- Numerics changes:
- Semi Lagrangian fix for polar vortex instabilities;
- Several code modifications to prepare the L91 version.
- Physics changes:
- Convection clean-up;
- Optimisation of linearised physics and more optimisations
of physics code;
- Oceanic Waves:
- Introduction of subgrid scale (unresolved) bathymetry effects;
- A fix to the EPS wave-model interface (Charnock variable)
- The overall impact is very small in terms of forecast performance.
- The parametrisation of the unresolved bathymetry has resulted in an
improved performance of the ocean wave system, while in the free atmosphere
a slight negative impact can be detected over the southern hemisphere
towards the later stages of the medium-range.
- The change to the new cycle is transparent for users apart from a
change in the atmospheric model
identification number in GRIB headers, which will be set to 122.
- The wave model identification numbers will also change and
will be:
- 114 for the Global Wave Model and
- 214 for the European Waters Wave Model.
29 June 2004 ECMWF implemented the Early
Delivery Forecasting System which comprises two main 6-hour 4D-Var analysis
and forecast cycles for 00 and 12 UTC (DA stream) with two additional
12-hour 4D-Var analysis (DCDA stream) and first guess forecast cycles.
These additional cycles are run with a delayed cut-off time of 14 hours
(with respect to the nominal analysis times). The analysis observation
windows are 21-09 UTC for the 00 UTC analysis and 09-21 UTC for the 12
UTC analysis. The first guess forecasts are used to initialise the main
operational 00 and 12 UTC assimilation and forecast cycles. Trials have
shown that the quality of the two first guesses is sufficiently high to
allow an early running of the 6-hour 4D-Var assimilations at around 0400
and 1600 UTC without any loss in quality in the ensuing forecasts compared
with the previous operational system.
- ECMWF products are now provided some three to four hours earlier in
line with the timing of the Early Delivery Forecasting System.
- The change to the new cycle is transparent for users apart from a
change in the atmospheric model
identification number in GRIB headers, which will be set to 123.
- The wave model identification numbers will also change and
will be:
- 115 for the Global Wave Model and
- 215 for the European Waters Wave Model.
28 September 2004 Intoduction of
Cycle 28r3.
- Physics:
- Revised convection scheme numerics and calling of the cloud scheme
- Use of tangent linear and adjoint of vertical diffusion in the
1st minimization of 4D-Var
- Reduction of radiation frequency to 1 hour in the high-resolution
forecasts
- Improved numerics of surface tile coupling
- Post-processing of total- column liquid water and ice.
- Satellite:
- RTTOV-8
- Minor revisions to ATOVS and AIRS usage
- Assimilation of MSG clear-sky radiances and GOES 9 BUFR AMVs
- Assimilation of SCIAMACHY ozone products from KNMI
- Correct error in AMSU-B usage over land
- Activate EARS data.
- Data assimilation:
- Blacklist SYNOP humidity data at local night time (solar elevation
SOE less than zero)
- Increased use of radiosonde humidity: use RS90 to -80C, RS80 to
-60C, other sensors to -40 C
- Proper cycling of the information from the wave altimeter and
the surface data analyses (FG forecasts moved from 00 and 12 UTC
to 06 and 18 UTC)
- EPS:
- Gaussian sampling for extra-tropical singular vectors (instead
of selection and rotation)
- Revision of initial condition perturbations for tropical cyclones
(TC)
- Initial condition perturbations extended to latitude belt
40 S 40 N (from 25 S 25 N)
- Tropical singular vectors are computed in the subspace orthogonal
to the leading 25 extra-tropical singular vectors
- New algorithm to determine optimisation regions based on predicted
TC tracks from previous EPS run
- The Caribbean remains an optimisation region if no TC in the
vicinity
- Ortho-normalisation applied to set of all tropical SVs
- Verification results gathered to date from the experimental suite
and from several months of research experiments in winter and summer
indicate that, in general, the impact of the new cycle is neutral to
slightly positive in the extra-tropical troposphere in the deterministic
forecasting system for the total sample of experiments. Wind and temperature
scores in the tropical troposphere show small improvements, but stratospheric
temperature biases are slightly larger. This issue is being addressed.
- There are, however, noticeable changes in the EPS. The revision of
initial condition perturbations for TCs, including the use of tropical
cyclone tracks from the previous EPS run, improves the TC track forecasting
giving a better spread and skill in the strike probability. The revised
numerics in the convection scheme and calling of the cloud scheme has
reduced the performance differences between the T511 forecast and the
T255 control. The previously experienced tendency in the EPS to develop
spuriously deep lows has been reduced, providing better synoptic guidance
with a smaller spread without affecting the overall skill of the EPS.
Users also need to be aware of the changes in the generation of initial
EPS perturbations. With the introduction of the Gaussian sampling the
one to one positive and negative perturbations will no longer be present.
- archive and disseminate step 0 for the deterministic forecast (as
this is used in the generation of weather parameter products)
- omit production of step 0 for BC project forecasts (was available
in FDB only)
- omit production of step 3 and 9 for eps control forecasts (to overcome
a inconsistency between the control forecast and the perturbed forecasts
and allow comparison of cumulative and mean fields)
- archive tropical cyclone tracks in BUFR format in MARS
- The change to the new cycle is transparent for users apart from a
change in the atmospheric model
identification number in GRIB headers, which will be set to 124.
|
